Among image devices including image recording devices such as printers and image reading devices such as scanners, there are image devices in which a movable body is moved back and forth within a predetermined range in the apparatus. For example, in inkjet printers, which are image recording devices, an ink head and ink cartridge, which are recording portions, are loaded on a carriage, which is a movable body, and that carriage is moved back and forth in a direction perpendicular to the transport direction of a recording medium such as paper. The carriage moves back and forth in a range that the ink head faces the entire image forming face of the recording medium in the direction perpendicular to the transport direction.
Thus, in the internal portion of the inkjet printer, a guide shaft is fixed whose longitudinal direction has been matched with the direction perpendicular to the transport direction of the recording medium. This guide shaft passes through a shaft bearing provided in the carriage. The movement direction of the carriage is prescribed to be the longitudinal direction of the guide shaft.
Ordinarily, in the carriage, the shaft bearing that the guide shaft penetrates is disposed in a position biased upstream or downstream in the transport direction of the recording medium from the center of gravity of the carriage, such that the guide shaft does not interfere with the ink cartridge or ink head loaded on the center portion of the carriage. Thus, a rotational moment centered on the guide shaft acts on the carriage. Also, forces that raise one end of the carriage in the direction of movement due to inertial force when accelerating or decelerating, and that rotate the carriage in a horizontal plane including the guide shaft, act on the carriage, which moves along the guide shaft. When the carriage is displaced in a direction other than the direction of movement along the guide shaft due to the action of these forces, the interval between the ink head and the image forming face of the recording medium changes, not only generating noise and vibration when the carriage moves, but also leading to a decrease in image quality because the image forming state is not fixedly maintained.
Consequently, in an ink jet printer, the carriage is fixed with respect to a direction of rotation centered on the guide shaft in order that rolling due to rotational moment in the carriage, and pitching and yawing due to inertial force when accelerating or decelerating, will not occur.
As an example of a configuration for this purpose, there are ink jet printers in which two guide rails are disposed parallel to the guide shaft, and a pressing member and a rotation stopping member that slide on each guide rail are provided in the carriage. Due to the pressing member pressing against one of the guide rails with a predetermined pressing force, rotational force in one direction that is centered on the guide shaft acts on the carriage. Due to the rotation stopping member contacting the other guide rail in the direction of this rotational force, the position of the carriage is fixed with respect to the direction of rotation centered on the guide shaft.
In this way, it is assumed that the guide shaft does not dislocate at the shaft bearing in a direction perpendicular to the direction of movement of the carriage, in order to reliably prevent carriage rotation centered around the guide shaft by putting the rotation stopping member and the pressing member in contact with the two guide rails.
On the other hand, ink jet printers have been proposed in which, in order to make it unnecessary to strictly maintain machining accuracy with the guide shaft, as the shaft bearing provided in the carriage, at least two inclined faces that contact an arc portion that constitutes a cross-section of the guide shaft are provided that contact the guide shaft at only two points in the cross-section (for example, see Patent Document 1).
In the configuration disclosed in Patent Document 1, by setting angles formed by a tangential direction and a perpendicular direction on the outer circumferential face of the guide shaft at the two contact points between the shaft bearing and the guide shaft such that frictional force generated between the guide shaft and the shaft bearing becomes larger than the force that attempts to slide the bearing shaft along the circumferential direction of the guide shaft during acceleration or deceleration of the carriage, the carriage is driven in a state in which a predetermined precision is maintained relative to the guide shaft.
Thus, in the configuration disclosed in Patent Document 1, along with controlling rotation of the carriage around the guide shaft, a guide rail is further provided that guides the carriage such that it is driven back and forth in the direction of the intersecting direction, and the angles are set according to the weight of the carriage, the position of the center of gravity of the carriage relative to the guide shaft, the distance between shaft bearings respectively provided in approximately both end portions of the carriage, the coefficient of friction between the shaft bearing and the guide shaft, the position of a guide transmission portion of the carriage relative to the guide shaft, the position of the guide rail relative to the guide shaft, and the speed of acceleration or deceleration conferred on the carriage. Thus, the shaft bearing portion of the carriage is prevented from rising up from the guide shaft during acceleration or deceleration of the carriage, noise and vibration is suppressed when the carriage is accelerated or decelerated, and it is made possible to record an image quietly and with high precision.
It is also described that of the angles mentioned above, by adopting a configuration in which the angle formed by a tangential direction and a perpendicular direction on the outer circumferential face of the guide shaft at the contact point of the downstream side of the transport direction of the recording medium is smaller than the angle formed by a tangential direction and a perpendicular direction on the outer circumferential face of the guide shaft at the contact point of the upstream side of the transport direction, because the sliding load between the guide shaft and the shaft bearing diminishes, the amount of friction at the contact point of the shaft bearing can be suppressed to a minimum limit, and it becomes possible to improve the durability of the recording device.
However, according to the configuration disclosed in the aforementioned Patent Document 1, there is the problem that it is not possible to reliably control rolling, pitching, and yawing that is generated during acceleration and deceleration of the carriage that moves along the guide shaft. That is, with only the factors considered in the configuration disclosed in Patent Document 1, it is not possible to reliable determine the angle of the two inclined faces of the shaft bearing. Thus, vibration and noise are generated when the carriage moves, leading to a deterioration of the image forming state. This sort of problem occurs not only in image recording devices such as ink jet printers provided with a carriage that is loaded with an ink head and an ink cartridge and moves back and forth; it likewise also occurs in image reading devices such as scanners provided with a unit that is loaded with a lens and a light-receiving element and moves back and forth.
It is an object of the present invention to provide an image apparatus in which, by considering all of the factors that operate on a movable member that moves along a guide shaft, it is possible to reliably control rolling, pitching, and yawing generated when accelerating or decelerating the movable member. Patent Document 1: JP 2002-137481A